I am not sure if manufacturers determine what is marketed or if the manufacturers simply make what the consumer wants. A bit of both, no doubt. I think part of the reason why bikes are so different nowadays is because the consumers (beginner, kids, racer, etc.) are very different from yrs gone by.
One thing that is definitely different is that today's rider is less likely to be interested in learning how to repair and maintain his/her bike. More and more riders just "take it to the shop." While I am not saying this is a bad thing, in the 70's when I started, it seemed like we all worked on our own bikes, running to the LBS only when we couldn't figure something out or needed advice.
As a coach and someone who tries to help beginners, I can tell you it's tough to steer a new rider away from the so-called latest and greatest. Even though a lot of the new stuff is constantly failing, people continue to buy and even replace with the same type part that failed.
I don't know where I am going with this, but perhaps just to say that a lot of riders view their bikes as having a finite life span.......maybe like a pair of running shoes.
Wes Oishi
L.A.